It is the long range purpose of this project to study interactions and relationships between connective tissue macromolecules as a way to understand connective tissue formation and structure. The topics of present interest are: 1) The mechanism of collagen fibril formation in vitro. 2) High resolution electron microscopy of fibrils and early aggregates in collagen assembly. 3) Quasielastic light scattering. 4) The effect of noncollagenous molecules on collagen assembly in vitro. We have developed a reproducible in vitro assembly system and shown that collagen fibril formation is a multistep process. After an early initiation step that is not understood, linear assembly of thin filaments dominates, followed by lateral association of the filaments to form native collagen fibrils.